Cobalt(III)-promoted hydrolysis of a phosphate ester

Anderson, Bill; Milburn, Ronald M.; Harrowfield, John M.; Robertson, G. B.; Sargeson, Alan M.

doi:10.1021/ja00450a042

Cited by 79 publications

(31 citation statements)

References 8 publications

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“…The 6-membered chelate ring lies in the same plane as the coordinated O atoms, and chelation of the HPO 4 2À ligand is confirmed. The O1-Co1-O2 angle of 76.118 is comparable to that found in other structurally characterized mononuclear Co III complexes containing chelated phosphate-these range from 75.468 to 76.608 [27][28][29][30] 1.540 to 1.548 ). [31] This lengthening is consistent with protonation at an exo (uncoordinated) O atom, and a careful search of the Fourier map found a peak attributable to an H atom close to only this O atom.…”

supporting

confidence: 81%

“…The 6-membered chelate ring lies in the same plane as the coordinated O atoms, and chelation of the HPO 4 2À ligand is confirmed. The O1-Co1-O2 angle of 76.118 is comparable to that found in other structurally characterized mononuclear Co III complexes containing chelated phosphate-these range from 75.468 to 76.608 [27][28][29][30] -and the overall geometry of the chelated HPO 4 2À ligand is quite similar to the chelated PO 4 3À ligands in these complexes. The most notable exception is the P-O exo bond to the protonated O atom; at 1.553 , this is significantly longer than the P-O exo bonds in the other complexes (range from 1.499 to 1.523 ) and is comparable to the P À O bond lengths in the dimeric complex [(trpn)COMMUNICATION 1.540 to 1.548 ).…”

supporting

confidence: 80%

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A Structural Model for HPO₄²⁻ Binding to Co in a Water Oxidation Catalyst

McClintock

Blackman

2010

Chemistry An Asian Journal

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Dedicated to the memory of Alan M. Sargeson, FAA, FRACI, FRS (1930-2008 The recent isolation by Kanan and Nocera [1,2] of a cobaltcontaining catalyst for water oxidation from electrolysis of a phosphate-buffered aqueous solution containing Co II ions represents a conspicuous success in the quest for practical and affordable methods of solar energy storage. While unable to unambiguously characterize the catalyst, they showed that it contained, in addition to P and K, Co (in either the 2+ or 3+ oxidation state) bound to oxygen, with a peak at 133.1 eV in the XPS spectrum consistent with the presence of the hydrogen phosphate anion, HPO 4 2À . [3] They proposed that HPO 4 2À was important in deprotonating an intermediate formed prior to O 2 evolution, and also in the self-repair of the catalyst through continual deposition and dissolution processes. [4] Subsequent EXAFS [5] and EPR [6] studies are consistent with phosphate (in an undefined protonation state) ligation to cobalt in the catalyst. Given that the solid catalyst appears to contain both Co and HPO 4 2À , and that HPO 4 2À is of importance in the aqueous phase, studies of the chemistry of Co species and HPO 4 2À in aqueous solution could be of importance in characterizing the water oxidation catalyst and may ultimately assist in determining the mechanism of O 2 evolution.Despite its apparent simplicity, the coordination chemistry of HPO 4 2À has been little explored; there are surprisingly few examples of crystallographically characterized mononuclear metal complexes containing monodentate HPO 4 2À [7][8][9][10][11][12][13] and none containing chelated HPO 4 2À . The latter observation is presumably related to the fact that complexes containing chelated PO 4 3À are unstable in aqueous acidic solution, undergoing rapid chelate ring-opening to give monodentate phosphate species. [9] Herein, we report the synthesis and characterization of the Co III complex [(pmea)Co- [14][15][16] ), the first crystallographically characterized example of HPO 4 2À acting as a chelating ligand in a mononuclear transition-metal complex. PO(OH))]ClO 4 (1) was prepared by reaction of [(pmea)CoCl 2 ]Cl [17] with NaH 2 PO 4 in water. The pink solid obtained following reduction in volume was crystallized in the presence of NaClO 4 to give X-ray quality crystals of 1 in reasonable (23 %) yield. Microanalytical data were consistent with the formulation of 1, thereby requiring a 1+ charge on the cation and consequently coordination of chelated HPO 4 2À , rather than the more usual chelated PO 4 3À . The observation of three peaks in the aliphatic region of the 13 C NMR spectrum of 1 was consistent with exclusive formation of the 6 geometric isomer; [18,19] such a preference has been observed previously in complexes containing the pmea ligand. A single peak at 20.2 ppm in the 31 P NMR spectrum of 1 confirms chelation, rather than monodentate coordination, of the HPO 4 2À ligand in D 2 O solution, [20] while the 59 Co NMR chemical shift of 9064 ppm is slightly greater than that of [(pmea)...

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supporting

confidence: 81%

“…The 6-membered chelate ring lies in the same plane as the coordinated O atoms, and chelation of the HPO 4 2À ligand is confirmed. The O1-Co1-O2 angle of 76.118 is comparable to that found in other structurally characterized mononuclear Co III complexes containing chelated phosphate-these range from 75.468 to 76.608 [27][28][29][30] -and the overall geometry of the chelated HPO 4 2À ligand is quite similar to the chelated PO 4 3À ligands in these complexes. The most notable exception is the P-O exo bond to the protonated O atom; at 1.553 , this is significantly longer than the P-O exo bonds in the other complexes (range from 1.499 to 1.523 ) and is comparable to the P À O bond lengths in the dimeric complex [(trpn)COMMUNICATION 1.540 to 1.548 ).…”

supporting

confidence: 80%

A Structural Model for HPO₄²⁻ Binding to Co in a Water Oxidation Catalyst

McClintock

Blackman

2010

Chemistry An Asian Journal

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“…In comparison, acetylene and ethylene dissociate on the iron surface via CH x radicals with an activation energy of about 0.6 -1.4 eV. 50 Without experimental estimation of the activation energy, mass diffusion was proposed as the limited process by Zhu et al 23 and Louchev et al 35 These results illustrate the diversity between the attributed underlying mechanisms that determine the apparent activation energy. It is fair to say that the growth process is not fully understood and the variation of the activation energy between 0.1 and 2 eV reflect the strong influence that different process parameters have on the growth mechanism.…”

Section: Growth Rate and Activation Energymentioning

confidence: 99%

Kinetics of laser-assisted carbon nanotube growth

Burgt

Bellouard

Mandamparambil

2014

Phys. Chem. Chem. Phys.

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Laser-assisted chemical vapour deposition (CVD) growth is an attractive mask-less process for growing locally aligned carbon nanotubes (CNTs) in selected places on temperature sensitive substrates. The nature of the localized process results in fast carbon nanotube growth with high experimental throughput. Here, we report on the detailed investigation of growth kinetics related to physical and chemical process characteristics. Specifically, the growth kinetics is investigated by monitoring the dynamical changes in reflected laser beam intensity during growth. Benefiting from the fast growth and high experimental throughput, we investigate a wide range of experimental conditions and propose several growth regimes. Rate-limiting steps are determined using rate equations linked to the proposed growth regimes, which are further characterized by Raman spectroscopy and Scanning Electron Microscopy (SEM), therefore directly linking growth regimes to the structural quality of the CNTs. Activation energies for the different regimes are found to be in the range of 0.3-0.8 eV.

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“…The use of metal complexes that mimic the structure and function of a metalloenzyme is a well-established approach in bioinorganic chemistry to develop highly effective catalysts modeled after nature and to gain a molecular level understanding of the enzymatic mechanism. In the late 1970s and 1980s pioneering work by the groups of Sargeson (Anderson et al, 1977; Jones et al, 1983; Hendry and Sargeson, 1989), Breslow (Gellman et al, 1986; Breslow et al, 1989), and Chin (Chin, 1991) among others gave the first insight into the role of the metal ion(s) in the mechanisms of phosphoester hydrolysis by metallohydrolases. Using phosphate esters with good leaving groups and kinetically inert mononuclear Co(III) complexes, metal-catalyzed hydrolysis reactions were shown to proceed through the following mechanisms: (i) Lewis acid activation, in which the metal polarizes the P-O bond and activates the phosphorus for nucleophilic attack (Figure 1A); (ii) metal hydroxide activation, in which the metal generates (metal-bound) hydroxide to act as an efficient nucleophile at pH 7 or as a general base (Figures 1B,C); (iii) stabilization of the leaving group (Figure 1D); and (iv) combinations of (i), (ii), and (iii).…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Studies of Homo- and Heterodinuclear Zinc Phosphoesterase Mimics: What Has Been Learned?

Erxleben

2019

Front. Chem.

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Phosphoesterases hydrolyze the phosphorus oxygen bond of phosphomono-, di- or triesters and are involved in various important biological processes. Carboxylate and/or hydroxido-bridged dizinc(II) sites are a widespread structural motif in this enzyme class. Much effort has been invested to unravel the mechanistic features that provide the enormous rate accelerations observed for enzymatic phosphate ester hydrolysis and much has been learned by using simple low-molecular-weight model systems for the biological dizinc(II) sites. This review summarizes the knowledge and mechanistic understanding of phosphoesterases that has been gained from biomimetic dizinc(II) complexes, showing the power as well as the limitations of model studies.

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Cobalt(III)-promoted hydrolysis of a phosphate ester

Cited by 79 publications

References 8 publications

A Structural Model for HPO₄²⁻ Binding to Co in a Water Oxidation Catalyst

A Structural Model for HPO₄²⁻ Binding to Co in a Water Oxidation Catalyst

Kinetics of laser-assisted carbon nanotube growth

Mechanistic Studies of Homo- and Heterodinuclear Zinc Phosphoesterase Mimics: What Has Been Learned?

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Cobalt(III)-promoted hydrolysis of a phosphate ester

Cited by 79 publications

References 8 publications

A Structural Model for HPO42− Binding to Co in a Water Oxidation Catalyst

A Structural Model for HPO42− Binding to Co in a Water Oxidation Catalyst

Kinetics of laser-assisted carbon nanotube growth

Mechanistic Studies of Homo- and Heterodinuclear Zinc Phosphoesterase Mimics: What Has Been Learned?

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A Structural Model for HPO₄²⁻ Binding to Co in a Water Oxidation Catalyst

A Structural Model for HPO₄²⁻ Binding to Co in a Water Oxidation Catalyst